HERMS Electric Brewing Explained: HLT, Mash Tun, Boil Kettle and Lautering

HERMS stands for heat exchange recirculating mash system. It is the way most three-vessel breweries, from 10-gallon home systems to 20-barrel production brewhouses, hold and change the temperature of a mash without ever putting heat directly on the grain. This post explains how it works, what each of the three vessels does, and what a brew day looks like on one. It replaces the five separate posts we used to have on the subject.

The idea in one paragraph

A coil of stainless tube sits inside the hot liquor tank, under the water. Wort is pumped out of the bottom of the mash tun, through that coil, and back on top of the grain bed. The water in the tank is held at a precise temperature by an electric element and a controller. As the wort passes through the coil it picks up the water's temperature, so the mash slowly and evenly comes to match the tank. Turn the tank up two degrees, and the mash follows. Nothing scorches, because the heat comes from water, not from an element or a flame under the grain.

The three vessels

Hot liquor tank (HLT)

"Liquor" is brewer's language for water. The HLT heats the strike water for mashing in, heats the sparge water, and houses the HERMS coil. On an electric system the element is in the HLT, so this is where the power goes. The DrainPro HLT takes a standard tri-clamp element, and the coil mounts through a compression-to-tri-clamp adapter rather than a weld, so it lifts out for cleaning or replacement.

Because the mash temperature follows the HLT, the HLT is usually held a degree or two above the mash target. That offset is how you steer.

Mash tun

Crushed grain and hot water sit here for an hour while enzymes turn starch into sugar. A false bottom holds the grain bed above the outlet so wort can drain from under it. The mash tun on a HERMS needs an outlet at the bottom for recirculation, a return port at the top, and enough headroom to add sparge water. The DrainPro mash tun has a welded 1.5" tri-clamp bottom drain, side recirculation ports, and, on 20-gallon and larger, a hinged side door so spent grain shovels straight out.

Mash temperature decides the beer. 148 to 150°F favours beta-amylase and gives a dry, highly fermentable wort. 156 to 158°F favours alpha-amylase and leaves more body. A HERMS holds either to within a degree for the whole rest, which a cooler or an insulated kettle cannot.

Boil kettle

After the mash, wort is drained and rinsed (that is lautering, below) into the boil kettle, brought to a rolling boil for 60 to 90 minutes with a second element, hopped, whirlpooled and chilled. The boil kettle's job is simpler than the other two vessels: heat, hold, and drain clean. A bottom-drain boil kettle with a whirlpool port spins the hop and break material into a cone in the centre and pulls clear wort from outside it, which leaves almost nothing behind after knockout.

What the coil actually does

Three things, and brewers who have never used one usually only expect the first:

• Holds temperature. Grain and water in an insulated kettle drift down a couple of degrees an hour. A recirculating mash does not drift at all.
• Steps temperature. Raise the HLT and the mash follows at about one to two degrees a minute on a 10-gallon system. Protein rests, beta rests, alpha rests and a mash-out to 168°F are a matter of typing numbers into the controller.
• Clarifies the wort. Recirculating for the whole mash sets the grain bed as a filter. By the time you lauter, the wort running off is bright. On a HERMS there is no separate vorlauf step because you have been doing it for an hour.

The trade-off, compared with a RIMS tube where an element heats the wort directly, is that a HERMS steps slower and needs a bigger water tank. In return it cannot scorch the wort, it cannot dry-fire an element if the flow stops, and the temperature it holds is very stable. For a system that will be used weekly for years, we think that is the right trade. If you want the single-vessel version of this argument, that is the Unibräu.

Lautering: mash-out, recirculate, sparge

Lautering is separating the sweet wort from the grain. On a HERMS it happens in three moves.

1. Mash-out. Raise the HLT so the mash climbs to 168°F. This stops the enzymes where you want them and thins the wort so it drains faster.
2. Recirculate. You have been doing this all along. The last ten minutes at mash-out temperature give you a clear, settled bed.
3. Sparge. Open the mash tun outlet to the boil kettle and, at the same rate, run 168°F water from the HLT onto the top of the grain through a sparge arm. The arm spreads the water across the whole bed so it rinses evenly instead of cutting a channel down one side. Match the rates so an inch of water always sits above the grain. Stop when the kettle has its pre-boil volume, or when the runnings drop below about 1.010, whichever comes first.

A sparge arm is for sparging only. Recirculation returns to a separate port, through a vorlauf arm, so the two jobs never fight over the same fitting.

Why electric

Gas heats faster and needs a garage door open. Electric heats predictably, indoors, with no flame under a stainless vessel full of sugar. The Bräu Supply HERMS runs both elements from one 240V, 30A circuit, up to 6 kW, through a three-vessel controller that also cuts power if the boil kettle is about to boil over. A steam condenser on the kettle lid turns boil-off back into water down a hose, so you can boil 20 gallons in a spare room without a vent hood.

A HERMS brew day, step by step

Timings are for a 10-gallon batch on a 10-gallon system. Bigger systems run the same order, a little slower.

Time	What you do	What the system does
0:00	Fill the HLT, set strike temperature (mash target + 10°F or so)	Element heats 12 gal in about 40 min
0:40	Pump strike water to the mash tun, mash in, set HLT to mash target + 1°F	Mash settles at 152°F
0:45	Start recirculating: mash tun out, through the coil, back on top	Holds 152°F, clarifies wort
1:45	Set HLT to 170°F for mash-out	Mash climbs to 168°F over 10 min
2:00	Open to the boil kettle, start the sparge arm	Wort drains, water rinses, 30 to 45 min
2:15	Switch the element to the boil kettle once it covers the element	Kettle heats while the sparge finishes
2:45	Boil, add hops, condenser on	60 to 90 min rolling boil
4:00	Flameout, whirlpool 10 min, run wort through the counterflow chiller to the fermenter	Pitching temperature in one pass
4:30	Recirculate hot cleaner through all three vessels and the coil	Done

Two pumps make this smoother: one on the mash tun for recirculation and sparging, one on the HLT for water transfers. Our system ships with both.

Cleaning the coil

The coil only ever sees wort on the inside and water on the outside. After the brew, recirculate hot cleaner through it the same way the wort went, then rinse. Once a year, pull it out through the tri-clamp adapter and look. In practice it stays clean, because nothing in it ever burns.

Planning the power? Our free electric brewery calculator sizes the breaker, wire and outlet for your elements and shows heat-up times.

Is a HERMS right for you?

Yes if you brew 10 gallons or more, want step mashes and repeatable numbers, plan to brew for years, or are looking at a pilot system for a brewery. The batch sizes go from 10 gallons to 50 gallons, one barrel finished, on the same design.

Probably not if you brew 5 gallons a few times a year, have limited space, or want the simplest possible brew day. A single-vessel Unibräu gets you 90% of the results in one kettle and a third of the floor space.

Building a HERMS out of vessels you already own? The parts are here: HERMS coil kit, DrainPro HLT, mash tun and boil kettle, all tri-clamp, all sized 10 to 50 gallons. Or ask us what fits what you have.